1. Field of the Invention
The present invention relates to a transmission line connection structure for use in a high frequency band such as a microwave band, a millimeter wave band or the like, a high frequency module provided with the transmission line connection structure, and a communication device using the module.
2. Description of the Related Art
Ordinarily, when a high frequency module is made up of discrete parts, it is necessary to connect transmission lines between the respective parts. Conventionally, connections between micro-strip lines, and connections between slot lines, are carried out by wire or ribbon bonding or the like.
FIGS. 11A and 11B show a conventional connection structure between micro strip lines. FIG. 11A is a perspective view of the connection structure. FIG. 11B is a plan view thereof. Here, strips 5a and 5b made of conductive patterns are formed on the upper faces of dielectric substrates 1a and 1b, respectively, and ground electrodes are formed on the under faces, whereby micro strip lines are formed. The end faces of the dielectric substrates constituting the two micro strip lines are opposed to each other, and the strips 5a and 5b are connected by bonding with a wire 15.
FIGS. 12A and 12B illustrate a connection structure between slot lines. FIG. 12A is a perspective view of the connection structure. FIG. 12B is a plan view thereof. Electrodes 2a and 2b having slots 3a and 3b are formed on the upper faces of the dielectric substrates 1a and 1b, whereby slot lines are formed, respectively. The end faces of the two dielectric substrates 1a and 1b constituting the slot lines, respectively, are opposed to each other, and the electrodes are connected by the wires 12.
FIG. 13 shows the return loss characteristics of transmission line connection structures in which the connection wires are provided in two different positions.
The connection structure in which the transmission lines are connected by wire or ribbon bonding, as described above, is greatly affected by a parasitic component caused by the connection of the wire or ribbon. For example, the impedances of the transmission lines may be mismatched in the connection portion, and the electromagnetic field distribution of the transmission mode may be disturbed. As a result, the electrical characteristics of the connection portion are deteriorated, and the return loss becomes significant as seen in FIG. 13. Especially, in a high frequency band such as a millimeter wave band or the like, the characteristics in the connection portion of the transmission lines are considerably deteriorated. This is one of the factors that reduce the performance of a module, or of a whole apparatus including the module.
Moreover, the structure in which transmission lines are connected by wire or ribbon bonding can suffer stress in the connection portion, which is caused by environmental changes or the like. As a result, the wire or ribbon is cut and the connection characteristic is changed. This may be another factor which causes the reliability to decrease.
Moreover, in the case of the connection structure obtained by wire or ribbon bonding, the connection between the transmission lines is fixed. Accordingly, once the transmission lines are connected to each other, parts equipped with the transmission lines can not be cut and separated from each other. Thus, problematically, adjustment or exchange on a part unit level is impossible.
In order to address the foregoing problems, the present invention provides a transmission line connection structure which prevents deterioration of the characteristic in the connection portion between transmission lines, solves problems such as reduction of the reliability in a bonding portion, change of the connection characteristic or the like, caused by environmental changes, and allows connection or disconnection between the transmission lines to be repeatedly carried out. The invention also provides a high frequency module provided with the transmission line connection structure, and a communication device using the module.
According to an aspect of the present invention, there is provided a transmission line connection structure in which transmission lines each having a predetermined structural body are connected to each other. Resonators connected to the ends of the transmission lines are arranged at the end portions of the respective structural bodies, and the end portions of the structural bodies of the transmission lines to be connected are positioned near to each other, whereby the resonators are electromagnetically coupled to each other. In this structure, it is unnecessary to connect the conductors of the two transmission lines by use of a wire or ribbon. That is, the transmission lines can be connected, without being affected by a parasitic component caused by the wire or ribbon. Moreover, in the structure, the transmission lines are arranged in such a manner that the resonators at the ends of the transmission lines are positioned near to each other. Thus, the connection and disconnection of the transmission lines can be repeatedly carried out.
The transmission lines may each advantageously comprise an electrode having a slot pattern formed on a dielectric substrate, e.g., as slot lines, fin lines, plane dielectric transmission lines (hereinafter referred to as PDTL, briefly) each comprising a dielectric substrate having slot patterns formed on both of the faces of the substrate in opposition to each other, and so forth.
Also advantageously, the transmission lines may each comprise strip-shaped electrodes formed on a dielectric substrate, e.g., as strip lines, micro strip lines, coplanar guides, suspended lines, and so forth.
Moreover, advantageously, the transmission lines may each comprise a dielectric strip arranged between two substantially parallel conductor planes, forming dielectric transmission lines.
The two transmission lines to be connected may have any one of the above structures. Also, different types of transmission lines may be connected. For example, a slot line and a micro strip line may be connected to each other.
Moreover, according to the present invention, a high frequency module may be formed, in which the above-described transmission line connection structure is applied to transmission lines to be connected between the various module components.
Furthermore, according to the present invention, a communication device such as a mobile communication device, a millimeter wave radar device, or the like, may be formed, which uses the above-described high frequency module.